This invention relates generally to lubrication means enabling both metal and/or ceramic bearing surfaces to resist mechanical wear at elevated operating temperatures of at least 300.degree. C. and higher, and more particularly to employing an improved source of lubrication as the means for doing so.
Lubrication is a well recognized means to reduce friction and wear between bearing surfaces in dynamic physical contact. As such, a pair of load bearing surfaces having relative movement therebetween will be in rolling or sliding contact, as well as combinations thereof, which can include a wide variety of known structural articles such as journal bearings, piston rings, gears, cams and the like. Two major areas for which improved lubricants are needed for continued progress at elevated temperatures are metal forming and transportation. Better metal forming capabilities to minimize machining and grinding require lubrication techniques and lubricants that can be used effectively at temperatures approaching the melting points of the metals now being used. In transportation, one of the most productive areas for increasing energy efficiency is often referred to as high temperature engines wherein temperatures range from 300.degree. C. and above making the selection of lubricants and means of lubrication difficult. In other known bearing applications high bearing contact pressures of 70,000 PSI are experienced making lubrication most difficult with existing lubricant systems. A known technique for lubrication at such high bearing temperatures and pressures is the use of solid lubricants in the form of plasma sprayed coatings of the metals and ceramics being employed.
Various organic lubricants which are applied as liquids at elevated temperatures of bearing operation are already known. For example, a published article entitled "Properties of a New Class of Polyaromatics for Use as High-Temperature Lubricants and Functional Fluids" ASLE Transactions Volume 9, Issue 1, pages 13-23 reports development of organic liquids for lubrication at elevated temperatures to include polyphenyls, polyphenyl ethers and polyphenyl thioethers. Subsequent investigations employing the latter lubricant are further reported in NASA Publications entitled "Formulation and Evaluation of C-Ether Fluids as Lubricants Useful to 260.degree. C." dated Dec. 16, 1980 and NASA Technical Memorandum 83474 entitled. "High Pressure Liquid Chromatography: A Brief Introduction, and Its Application in Analyzing the Degradation of a C-ether (Thioether) Liquid Lubricant" dated Sep. 1983. In both NASA publications, degradation of the starting thioether lubricant was found to occur at elevated temperatures of bearing operation, however, limiting the use temperature of this lubricant to no greater than 260.degree. C.
More recent developments whereby a polymeric lubricating film is deposited on both ceramic and metal bearing surfaces from a vaporized polymer-forming organic reactant is also now known. For example, a tenacious polymer lubricating film is disclosed in U.S. Pat. No. 5,139,876 upon treating ceramic bearing surfaces during operation at elevated temperatures of at least 300.degree. C. with vaporized organic reactants such as petroleum hydrocarbon compounds, mineral oils, various synthetic lubricants and to further include tricresyl phosphate (TCP) and triphenyl phosphate. In a still more recently issued U.S. Pat. No. 5,351,786, there is further disclosed lubrication means for such operation of these bearing devices with polymer lubricants formed in-situ upon vapor-phase deposition of various phosphazene compounds. For the vapor-phase lubrication of ceramic bearing surfaces in such manner, it has also been found that formation of the desired polymer lubricant can possibly be further enhanced by ancillary means. Accordingly, U.S. Pat. No. 5,139,876 discloses formation of the lubricating film after first treating the uncoated ceramic surface at elevated temperatures with activating metal ions comprising a transition metal element selected from the Periodic Table of Elements to include iron and tin. There is similarly disclosed in U.S. Pat. No. 5,163,757 a lubrication means for ceramic bearing devices utilizing metal oxide lubricants formed during bearing operation. As therein disclosed, continuous lubrication of the ceramic bearing surfaces is provided with solid metal oxide lubricants formed in-situ with an oxidizable metal source located in physical proximity to the ceramic bearing surfaces being treated. A representative lubrication system enabling such mode of operation includes (a) support means causing the ceramic bearing surfaces to be maintained in dynamic physical contact, (b) an oxidizable metal source located in physical proximity to the support means, and (c) heating means for continuously heating the metal source while the ceramic bearing surfaces are being operated sufficient to provide the solid metal oxide lubricants. In one embodiment, the ceramic bearing means employs ceramic ball bearings supported within a ceramic race with a metal housing member enclosing the bearing structure. Utilizing oxidizable metals for construction of said housing member, including molybdenum and iron alloys, provides a suitable metal source in sufficient physical proximity to the bearing surfaces for satisfactory lubrication at the aforementioned operating conditions. Since it is expected that vapor-phase lubrication with the present lubricants can likewise be enhanced utilizing the same or similar ancillary means, the entire contents of both 5,139,876 and 5,163,757 prior art patents are hereby specifically incorporated by reference into the present application.
It remains desirable to provide lubrication of both metal and ceramic bearing means when operated at these elevated temperatures under various atmospheric conditions by still more effective means. Accordingly it is one object of the present invention to provide improved lubrication means for various type mechanical apparatus utilizing either metal or ceramic bearing materials, including combinations thereof, under such operating conditions.
It is another object of the present invention to provide means for continuous lubrication of metal and ceramic bearing surfaces with a novel class of vapor-deposited polymer lubricants formed in-situ.
A still further object of the present invention is to provide a novel method for the lubrication of metal and/or ceramic bearing surfaces at relatively low lubricant levels with vapor-phase deposited lubricants.
These and further objects of the present invention will become more apparent upon considering the following detailed description of the present invention.